1. Field of the Invention
The present invention relates to a blood circuit for a dialysis machine.
As is known, blood consists of a liquid component, called the blood plasma, and a corpuscular component formed by the blood cells, including the red corpuscles among other types. In renal insufficiency, the blood contains, in addition to the aforesaid components, particles of low molecular weight (referred to below as the solute), which have to be eliminated by a dialysis treatment carried out by means of a dialysis machine.
A dialysis machine of a known type generally comprises a blood circuit, a dialysate circuit, and a filter which is connected to the aforesaid circuits and comprises a blood compartment and a dialysate compartment, which are separated from each other by a semi-permeable membrane, and through which pass, respectively, the blood to be treated and the dialysate, generally flowing in counter-current mode, when the machine is in operation.
During the dialysis treatment, the unwanted particles contained in the blood migrate from the blood compartment to the dialysate compartment both by diffusion and by convection, as a result of the passage of some of the liquid contained in the blood towards the dialysate compartment. The patient will therefore have lost some weight by the end of the dialysis process.
The blood circuit is connected to the patient by means of an arterial needle and a venous needle, which are inserted into a fistula formed in the patient's cardiovascular system, and are used, respectively, to collect the blood to be treated and to return the treated blood to the patient's cardiovascular system. The blood circuit comprises two expansion chambers (or droppers), one located in the arterial branch and one in the venous branch.
2. Background Art
In a known method for detecting the detachment of the venous needle from the patient and preventing blood loss due to the detachment of the venous needle, an electric current is injected into the blood circuit in such a way that the detachment of the venous needle is comparable to the opening of a circuit. Thus, by measuring the variation of electric current flowing in the blood circuit it is possible to detect the detachment of the venous needle.
For example, patent application WO 99/12588 describes a method in which the blood circuit is connected to an electrical circuit to inject a current into a closed circuit consisting of the blood circuit and the patient's cardiovascular system, and to measure, by means of a measuring instrument located in the aforesaid blood circuit, the variations of current caused by the detachment of one or both of the needles. In this method, the current injection and the measuring of the variation of current are carried out by means of inductive couplings located in the blood circuit, in other words by means of windings formed around the extracorporeal blood circuit at specified points of this circuit.
The placing of the windings around the blood circuit gives rise to problems of a practical nature, since the coupling between the blood circuit and the electrical circuit is laborious to set up and requires a certain amount of the operator's time.